1. Field of the Invention
The present invention relates to wireless communication devices capable of communicating through wireless communication systems which operate under different communication protocols.
2. Related Art
Various kinds of wireless communication devices are used for mobile communications. The devices include, for instance, personal digital cellular (PDC) type phones such as a cellular phone and a car phone, and personal handy phone (PHS) type devices developed as the second generation cordless phone.
The PDC phone is capable of providing communication services over a wide area because the service area of its base station (BS) is from 1.5 kilometers to several kilometers (macro cell) in radius, and is capable of providing communication services even when phone users are moving at high speeds. The cellular phones and the car phones consume more electric power. On the contrary, the PDC phone provides communication services over a limited area because the service area of its cell station (CS) is from 100 meters to several hundred meters (micro cell) and the phones consume less electric power. The PDC phone is not capable of providing its services when phone users are moving at high speeds.
New type of cellular phones which are compatible with both the PDC phone and the PHS phone are proposed so that such phones are operable under both of the PDC communication protocol and the PHS communication protocol. This requires new wireless communication service system operators which enable communications under both of the PDC system and the PHS system in addition to the conventional system operators which provide communication services of only one of the PDC system and the PHS system.
If a system operator provides communication services of both systems, a single phone number may be assigned to a cellular phone having both of the PDC communication function and the PHS communication function as a PDC phone number to be used under the PDC system and a PHS phone number to be used under the PHS system. Alternatively, a PDC phone number and a PHS phone number may be managed by bringing the numbers into proper correlation even if the numbers are different from each other. As a result, it is possible for such a system operator to control communication switching operations in the PDC system and in the PHS system in a unified manner.
If the communication services under the PDC system and the PHS system are separately provided by different system operators, on the other hand, it is impossible to assign the single phone number to the cellular phone having both of the PDC communication function and the PHS communication function as the PDC phone number and the PHS phone number. It is also impossible to correlate the PDC phone number and the PHS phone number. Thus, it is impossible to control the communication switching operations in both systems in a unified manner.
It is assumed that no operators provide communication services of both systems, and that cellular phones A, B and C are operable under both PDC and PHS systems, only PDC system and only PHS system. It is also assumed that a user of the phone C inputs the PHS phone number of the phone A to send a call signal to the phone A through a PHS communication network in the PHS system, while the phones A and B are in the communication state through a PDC communication network in the PDC system. The PHS communication network is incapable of checking whether the phone A is in communication with the phone B. It is therefore impossible to transmit to the phone C an answer message indicating that the phone A is in the communication state. Thus, the user of the phone C is not capable of checking the state of the phone A to which the call is addressed.
It is therefore an object of the present invention to provide a wireless communication device which is capable of notifying a communication state to a caller upon receipt of a phone call.
A compatible wireless communication device has both communication functions of different communication protocols. The device receives a call from one device through one communication network when it is in the communication with another device through another communication network operating under a protocol different from that of the one communication network. The compatible device changes its connection to the one communication network to transmit to the one device a fixed answer message indicating that it is in the middle of communication with the other device.
The fixed answer message may be transmitted automatically or in response to a predetermined key operation of a user of the compatible device. The existing communication with the other device may be continued irrespective of the call from the one device, or a new communication with the one device may be enabled in response to another predetermined key operation of the user while holding the communication with the other device to be resumed later.